linux-kernel - Re: [PATCH 03/10] irqchip/gic: Switch to dynamic chip name output

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Date:   Fri, 11 Feb 2022 09:08:43 +0000
From:   Marc Zyngier <maz@...nel.org>
To:     Linus Walleij <linus.walleij@...aro.org>
Cc:     linux-kernel@...r.kernel.org, linux-gpio@...r.kernel.org,
        Bartosz Golaszewski <brgl@...ev.pl>,
        Matthias Brugger <matthias.bgg@...il.com>,
        Grygorii Strashko <grygorii.strashko@...com>,
        Santosh Shilimkar <ssantosh@...nel.org>,
        Kevin Hilman <khilman@...nel.org>,
        Tony Lindgren <tony@...mide.com>,
        Thomas Gleixner <tglx@...utronix.de>,
        Vladimir Zapolskiy <vz@...ia.com>,
        Andrew Lunn <andrew@...n.ch>,
        Gregory Clement <gregory.clement@...tlin.com>,
        Sebastian Hesselbarth <sebastian.hesselbarth@...il.com>,
        Emil Renner Berthing <kernel@...il.dk>,
        kernel-team@...roid.com
Subject: Re: [PATCH 03/10] irqchip/gic: Switch to dynamic chip name output

On Thu, 10 Feb 2022 23:38:49 +0000,
Linus Walleij <linus.walleij@...aro.org> wrote:
> 
> On Wed, Feb 9, 2022 at 5:26 PM Marc Zyngier <maz@...nel.org> wrote:
> 
> > The last dynamic aspect of the GIC's irq_chip structure is the
> > name that is associated to it.
> >
> > Move the output of that name to the relevant callback, which
> > allows us to do a bit of cleanup and mark the structures const.
> >
> > Signed-off-by: Marc Zyngier <maz@...nel.org>
> 
> Reviewed-by: Linus Walleij <linus.walleij@...aro.org>
> 
> This naming was once introduced for the ARM PB11MPCore
> that had two cascaded GICs (commit 58b8964990dc6)
> so it became a pain to see which one
> was being used in /proc/interrupts
> arch/arm/boot/dts/arm-realview-pb11mp.dts
> 
> I see it is not appreciated to use /proc/interrupts for this
> type of diagnostics. Ugh. I suppose people do it for the
> same reason they keep using the GPIO sysfs, they like
> it and they know it.

It was sort of fair game to use /proc/interrupts to track these things
when we only had that. These days, we have a whole interrupt debugging
infrastructure that is able to track hierarchies, domains and other
state. And it isn't like we're taking away the /proc/interrupts
facility at all, we only indirecting the name output it when possible.

There are also a number of advantages in keeping these data structures
read-only when possible, in addition to the memory saving associated
with only having a reference to the irq_chip structure.

Thanks,

	M.

-- 
Without deviation from the norm, progress is not possible.